Sliding doors are usually of two-part construction with one door panel being fixed and the other door panel sliding relative to it. Such doors are in wide-scale use for residential and commercial construction. The door panels are usually frames, glazed, preferably with thermal glass panels. The frames are also required to have a degree of thermal efficiency at least equal to that of the glazing and preferably higher.
Various designs have been proposed and have been in considerable usage in the past, employing extruded plastic material such as vinyl plastics. Extrusions are also in wide use for the door jambs and cross frames.
The use of such extruded plastic material is attractive from the viewpoint of economy, and also since they may be extruded in various colours, and are resistant to weather damage and the suns rays, and also have a low thermal conductivity. However, they do have certain disadvantages. In the first place, the past extrusions have been of relatively simple cross-section. Such extrusions have often had insufficient strength to carry the weight of a heavy glass panel in a full size sliding door, and have been subject to warping or bending.
In addition, the provision of a good air seal between the door frame and the door jambs has not always been satisfactory in the past.
Furthermore, the system for glazing the door frame did not always readily permit replacement of broken glass panels, and did not always provide for an adequate seal between the glass panel and the frame.